The present invention relates to an ink-transfer-type printer which transfers ink to a recording sheet (such as a plain paper) to form an image thereon.
Among printers which transfer ink onto a recording sheet such as plain paper, the following printers are known: an ink jet printer that jets ink onto a recording sheet from nozzles as liquid droplets, a thermal transfer printer that heats an ink ribbon (which can be melted by heat) using a thermal head, thereby to transfer the ink onto a recording sheet; and a wire impact dot matrix printer that uses a steel wire for striking ink ribbons against a recording sheet.
However, these known printers have following problems: the ink jet printer may encounter clogging of ink in the nozzle; the thermal transfer printer may increase running cost due to the consumption of ink ribbons; and the wire dot printer is inferior in processing speed. Thus, a printer in which ink clogging is prevented, having a low running cost and a high processing speed has been desired.
In this connection, the present inventor has proposed an ink-transfer-type printer as disclosed in Japanese laid-open patent application No. Hei 10-799 published on Jan. 6, 1998. This printer comprises a ink roller constituted by covering a ink holding member with a film member which selectively allows the permeation of ink, and ink seeping out of the ink holding member through the film member is transferred onto a recording sheet. The film member is formed by uniformly dispersing additives in a matrix, the thermal expansion coefficient of which is larger than that of the additives.
Accordingly, when the film member is heated, the gap is formed around the respective additives due to the difference of the thermal expansion coefficients between the matrix and the additives. Thus, by heating the selected portions of the film member by means of a thermal head or the like, ink is able to seep out through the gaps formed at the heated portions, to be transferred onto a recording sheet to form a corresponding ink image thereon.
In the above ink-transfer-type printer, however, it is not easy to precisely control the operations of the printer, particularly to control the timing between heating the film member to form gaps in the film member and transferring the ink to the recording sheet.